The Long Term Evolution-Advanced (LTE-A) Rel-10/11/12/13/14 versions of the 3rd Generation Partnership Project (3GPP) are enhancements of the LTE Rel-8/9 versions. An LTE-A system has a higher bandwidth requirement than an LTE system, and supports a peak data rate of up to 1 G/s in a downlink and 500 M/s in an uplink. To meet a requirement of LTE-A, a carrier aggregation (CA) technology is used as a method for extending system bandwidth for the LTE-A system. In addition, a multi-antenna enhancement technology, that is, multiple-input multiple-output (MIMO), and a coordinated multipoint (CoMP) technology are used to improve a data rate and system performance.
With rapid development of wireless communications and emergence of ultra-high-rate services (such as high-definition videos), the load of a wireless communications network becomes heavier despite various technologies used in the LTE-A system to improve data rate. Thus, reducing the load of the network has become a research focus. Device-to-device (D2D) communication emerges accordingly, and becomes a key project of the LTE-A Rel-12/13 versions. In this direct device connection and communication mode, terminals may directly communicate with each other without forwarding by an eNB, thereby sharing data load of the eNB. D2D communication can better utilize a spectrum resource, and improves spectrum utilization and a data rate while reducing load of the eNB.
To improve spectrum utilization and make the most of a radio frequency capability of an existing terminal, multiplexing of a spectrum resource of an existing mobile communications network is considered for a D2D communication link (also referred to as a sidelink (SL)). To avoid interfering with a terminal in the existing network, downlink (e.g., a link from an eNB to UE) spectrum resources in LTE-A is not used in D2D communication. Instead, uplink (e.g., a link from the UE to the eNB) spectrum resources in the LTE-A system are multiplexed because interference immunity of an eNB is generally stronger than that of a typical UE. A D2D device is more likely to multiplex the uplink spectrum resource in a time division manner. In this way, simultaneous receiving and sending do not need to be supported, and only sending or receiving needs to be performed at a moment.
In a power control mechanism in the current system, transmit power of a mobile device is associated with a moving speed of the mobile device. Different moving speeds correspond to different transmit powers. A higher moving speed of the mobile device corresponds to a larger transmit power of the mobile device. A lower moving speed of the mobile device corresponds to a smaller transmit power of the mobile device. Determined transmit power is inappropriate because only impact of the moving speed on the transmit power is considered when the transmit power is determined. When transmitting data using the transmit power, the mobile device may interfere with another nearby mobile device. For example, if a mobile device (such as UE or a vehicle) with a relatively high moving speed uses relatively large transmit power when sending non-emergency data, another nearby mobile device that has a relatively low moving speed but needs to send an emergency data service is interfered with. For another example, it is also inappropriate if a mobile device with a relatively low moving speed uses a relatively small transmit power when sending emergency data. Consequently, a receive end may fail to receive the sent emergency data.